Just like in English, although maybe not here, the common verb often does not have to be explicitly written. The two equally correct answers are "Tämä on oikein ja tuo on väärin" and "Tämä on oikein ja tuo väärin".
I can't help but notice how oikein sounds a bit like okay. Coincidence or derivation? ^^
I would think the correct translation would be tama yksi on oikein. Etc. otherwise the sentence to translate would be this is correct and that is incorrect
No, yksi is not used like that in this context. Both this and this one translate to tämä.
But why not. To just say it is not used we don’t know what context it is used. How do we know when it is used?
why not celui ce ja celui la
Because this is the English course?
Those words have not been introduced to us in the lessons and tips